1. Field of the Invention
The present invention relates to a method for manufacturing a coated sheet. A method of this invention is useful in formation of, for example, an optical functional layer. In particular, this invention relates to an optical element using the optical functional layer concerned. The optical elements etc. are suitably utilized in various image display devices, such as liquid crystal displays (LCD), organic electroluminescence display devices, PDPs, and CRTs.
2. Prior Art
Conventionally, various kinds of coated sheets obtained by forming a coated layer by way of giving processes, such as coating, drying, etc. of a coating liquid onto a surface of a base material film have been manufactured. As coating method for the above-mentioned coating liquid, various methods, such as a slot die method, a reverse photogravure coating method, and a micro photogravure method, are adopted.
As coated sheets, for example, various kinds of optical films having optical functi nal layers may be mentioned.
In displays of OA equipment, such as TVs and desktop PCs, CRTs that have been conventionally in the mainstream are now being replaced by liquid crystal displays having large advantages of, such as being thin and light weight and of low power consuming. Liquid crystal displays now widespread comprise liquid crystal layers for forming retardation films, hard coat layers for surface protection, and surface treatment coated layers, such as antireflection films.
Optical functional layers are formed with thin films as request for upgraded performance of optical function is increased. When the thin film concerned has unevenness in film thickness, the unevenness decreases displaying capabilities of image viewing displays, such as liquid crystal display using the film. Therefore, it is required that optical functional layers should have uniform film thickness. However, in any coating methods, a flow of resin occurred in a transition period from a coating process to a drying process, and the flow of the resin made difficult formation of coated layer with a uniform film thickness. Accordingly, it was difficult to form a coated layer having a uniform film thickness on a base material film with a particularly wide area.
For example, when a hard coat layer, an antireflection layer, etc. are formed on a high polymer film, resin layers laminated have different refractive indexes, which lead to problem with serious coherence unevenness caused by thickness unevenness based on flow of the resin after coated. In this case, since differences arise in optical thickness within a surface, reflectance also gets smaller than a theoretical value.
In general, liquid crystal molecules forming a liquid crystal layer show tendency of being easily influenced by characteristics of an interface, and it is known that an interfacial regulating force, such as rubbing treatment, will accelerate alignment (orientation) of liquid crystal molecules based on aromatic groups. Since one side of a coated liquid including liquid crystal molecules is opened in case of the above-mentioned coating method, in usual coating and drying methods, air flow on the open side generates resulting orientation unevenness of the liquid crystal layer. Therefore, the liquid crystal layer obtained in this way has a problem that some portions of a liquid crystal display have unevenness in front contrast.